This invention relates to a fixture for expanding the tubes of a heat exchanger coil into holding contact with the tube sheets and heat exchanger fins of the coil and, in particular, to a tube expanding fixture that can accommodate heat exchanger coils of varying sizes with a minimum of change over adjustments.
As explained in detail in U.S. Pat. No. 4,646,548, during the production of a heat exchanger coil of the type typically employed in air conditioning units, thin heat exchanger fins are stacked between a pair of heavier tube sheets and hairpin tubes are passed through holes provided in the stack. A hairpin tube, as the name implies, is one that is bent at its midsection to provide two parallel legs of substantially equal length. The legs of the hairpins are passed through the coil stack and the hair pins are cojoined by tube bends to establish a refrigerant flow channel that passes back and forth through the coil. The coil can act either as a condenser or an evaporator in a refrigeration system.
During production of the coils, the hairpins are inserted into the coil stack and the assembly is then placed in a tube expander fixture. The expander fixture has a front door that opens so that a coil can be received within the fixture. A saddle is located in the lower part of the fixture that contains seats upon which the bends of the hairpins rest. The tubes are supported vertically in the housing with their open ends aligned beneath an array of expander rods which are sometimes referred to as "bullets". When the coil is properly mounted in the fixture, the door is closed and secured and the rods are passed downwardly into the tubes to expand the tubes into locking contact with the tube sheets and the fins.
The coil assembly must be properly supported during the expansion process to prevent the tubes from buckling or the assembly from otherwise being damaged. Heretofore, the fixture could handle heat exchangers up to a certain size, after which the back wall of the fixture had to be removed and replaced with a larger panel. This change over procedure was both time consuming and labor intensive, thus necessitating the use of a good deal of equipment and extensive down time. In addition, the back panel of the fixture typically is relatively a heavy piece and if improperly handled, can be dislodged causing damage to the equipment and potential harm to those attempting to replace the panels.
It has also been customary to increase the size of the housing door corresponding to an increase in the size of the back wall panel. This has been achieved by securing additional horizontal bar to the door so that the height of the door is substantially equal to that of the back panel. The addition of bars to the door, although easier and less time consuming to accomplish the replacement of the back panel, again take time and effort further increasing the expense of a change over.